Demand for mobile and wireless communication is increasing as users get more and more used to communicating using wireless communication devices and as applications suitable for a mobile environment are developed. This increases the demand for available bandwidth in wireless communication networks.
Furthermore, as users increasingly use public transportation in order to reduce transportation costs and in view of environmental opinions, the opportunity to use wireless and mobile devices during transportation increases. For instance, many users talk to friends, family or business connections, check emails, check web pages such as news sites, receive streaming music, watch films or TV broadcasts using media applications in the mobile devices during travelling to and from a location, e.g. commuting to and from work.
In the situation with commuting, several different access devices may be connected along the geographical route and each switch between access devices may trigger a series of control signaling and data signaling over an infrastructure network supporting the access devices.
In the increasing demand for bandwidth, control and data signaling is preferably reduced.
The continuously increasing traffic output of subscribers means higher and higher transport costs for the operators. As a result operators are willing to invest more and more in new techniques that enable more efficient transport utilisation.
In the 3G/SAE architecture the GGSN or the PDN-GW (from now on referred to simply as “GW”) is an anchor point for the mobile terminal. All traffic generated or received by the terminal has to pass through the GW, as the GW is the IP “point of presence” of the terminal for the external world.
If the gateway is far away from the mobile terminal, it requires considerable transport usage to get traffic to/from the terminal, especially in the frequent case when the terminal communicates with geographically close partners. This waste of transport resources is called a tromboning effect. By putting a local GW close to a group of base stations it is possible to eliminate unnecessary traffic tromboning for static subscribers. With such a solution, not only transmission cost may be spared but transit peering costs as well due to potential local peering options.
Unfortunately, such distribution of GWs may result in very long transport paths for subscribers that move away from the place of their initial attachment. Such users may be travelling businessmen or simple commuters.
State of the art mainly includes the existing mechanisms in 3GPP to select GWs when a subscriber attaches to the network. The DNS-based procedure is standardised for 3G networks while it is under standardisation for SAE (R8). In the standard, an S-GW is selected when the terminal attaches to the network and P-GW is selected during the attach procedure and also when the UE requests a new PDN Connection. The selection process in SAE is roughly the following:
1 Terminal attachment request
2 eNodeB sends attachment request to MME
3 MME receives attachment request—can infer subscriber identity as well as location (e.g. via eNodeB identity)
4 MME authenticates subscriber using HSS/HLR
5 HSS sends back name of default PDN context
6 MME resorts to DNS to obtain the candidate list of GWs
7 MME selects one of the GWs
The standard selection process can take into account goals like:                selection of a combined GW (a GW which is Serving and PDN-GW as well),        load sharing (e.g. in random or weighted random order)        geographical considerations (if APN names are provisioned to have a geographical context as well) DNS-based selection under standardization in 3GPP.        Topology        
Neither of the existing solutions is prepared for movements of subscribers. This means that the selection mechanisms do not take into account the potential user mobility and the expected traffic volumes at different locations.
Hence they cannot utilise transport so efficiently for a user who is mobile. On the contrary, selecting a local GW for a highly moving user may even be worse than selecting a further away (more centrally placed) GW.
In another example, in a scenario with a city centre and a suburb where all people leave their home in the morning to go to work in the city centre there may be enormous strain on the Radio and Core networks due to tracking area update (TAU) signalling at specific times during the day. For instance, Tokyo has this problem when Shinkansen travel and arrives into the city.
This has been tried to be counteracted in the 3GPP standard with the use of TAI lists (TAI list is an aggregation of several TAs)
Problems:
1) there is no clear picture on how to define the TAI lists.
2) There are also problems if the subscriber keeps the potentially huge TAI list during paging procedures, the paging request will be sent to a very large area.
3) If there is no defined end to the TAI list there will be a massive TAU storm when all the commuters arrive at the same time.